cleaned by siphoning fecal and any uneaten feed debris. For consumption measurements, Ž
. fish were fed one-half of their daily ration pre-weighed and allowed 30 min to
consume this quantity before siphoning uneaten feed into containers with a small-diame- ter hose. Feed and water obtained was filtered through pre-weighed coarse filter paper
with the aid of a vacuum pump. Samples were then dried at 60 8C overnight, weighed
and subtracted from the quantity initially provided to quantify feed intake. At the conclusion of the first experiment, one fish from each aquarium at each of five
time points, ranging from 0 to 16 h postprandial, was bled for plasma glucose analysis. Blood was first centrifuged for 5 min after which supernatant was removed with a
transfer pipette. This was then deproteinized with perchloric acid and neutralized with Ž
. potassium carbonate using the method of Brock et al. 1994 . Plasma samples were
Ž stored frozen at y80
8C until glucose was analyzed Sigma Kit a510; Sigma, St. Louis, .
MO . Additional sampling from the first experiment involved muscle and liver tissue Ž
. being excised, wrapped in foil and stored frozen y80
8C until being analyzed for proximate composition. Liver tissue from 2 and 16 h time points was also analyzed for
enzymatic activity as described later. Muscle, liver, and intraperitoneal fat were taken Ž
. from seven fish per aquarium one fish per aquarium from the second experiment for
Ž determination of the following body indices: hepatosomatic index HSI: liver weight =
. Ž
. Ž
. 100rBW , intraperitoneal fat IPF ratio IPF weight = 100rBW , and muscle ratio
Ž .
MR: muscle weight = 100rBW . Ž
. Glutamate dehydrogenase GLDH activity was determined using the procedure of
Ž .
Schmidt and Schmidt 1983 while glutaminase and glutamine synthetase activity were Ž
. analyzed using the procedure of Chamberlin et al. 1992 . All enzyme assays were run at
Ž .
28 8C and activity was expressed per milligram liver protein Lowry et al., 1951 .
Ž .
Differences between means were tested for significance P - 0.05 using the GLM Ž
. procedure
SAS Institute, 1985 . Duncan’s multiple-range test was used to detect significant differences among means.
3. Results
3.1. Effects of dietary energy leÕels 3.1.1. Fish growth and body condition indices
Survival was high for red drum fed all treatments in the first experiment with only the Ž
. Ž
. mean of fish fed the 18.4 kJrg diet 97 being less than 100 Table 2 . All diets
Ž resulted in weight gain of about 200 of initial weight during the 6-week period Table
. 2 . There were no differences in weight gain attributable to increases in dietary energy.
Feed efficiency for all fish ranged from 0.72 to 0.87 with no significant differences attributable to dietary energy. HSI was highest for fish fed the diet containing 16.7 kJrg
but it was not significantly greater than that of fish fed the two higher energy levels of 17.6 and 18.4 kJrg and lowest in fish fed the two diets with lowest energy concentra-
tions. IPF ratio also was lowest in fish fed the lowest energy concentration while all other diets resulted in similar IPF deposition. MR was fairly consistent ranging from
37.5 to 38.6 and was not significantly different at any dietary energy level.
Table 2 Production characteristics and body condition indices of red drum fed diets containing different energy levels
c,d c,e
c,f
Diet designation Weight gain
Feed Survival
HSI IPF ratio
MR
a,b
Ž Ž .
of initial efficiency
a
. weight
g,i i
45 CP: 15.1 kJ 207
0.80 100
1.3 0.5
38.4
i h
45 CP: 15.9 kJ 230
0.82 100
1.2 0.9
38.6
h h
45 CP: 16.7 kJ 227
0.87 100
1.6 0.8
37.7
h,i h
45 CP: 17.6 kJ 199
0.73 100
1.4 0.8
37.5
h,i h
45 CP: 18.4 kJ 231
0.81 97
1.4 1.0
38.1 Analysis of variance, P F
0.5302 0.3158
0.4516 0.0033
0.0149 0.6521
Pooled standard error 16.25
0.04 1.49
0.15 0.24
1.30
a
Values represent means of three replicate aquaria of fish with average initial weight of approximately 35 grfish and fed for 6 weeks.
b
g gainrg dry feed.
c
Values represent means of seven fish from each of three replicate aquaria.
d
HSI: liver weight=100rfish weight.
e
IPF ratio: intraperitoneal fat weight=100rfish weight.
f
MR: muscle weight=100rfish weight.
g
Ž .
Values within the same column with different superscripts h,i were determined to be significantly different Ž
. P - 0.05 by Duncan’s multiple-range test.
3.1.2. Tissue composition There was a tendency for relative liver protein to be higher in red drum fed the lowest
energy diet while the lowest liver protein was present in fish fed the highest energy diet Ž
. Ž .
although differences were not quite significant P s 0.0565 Table 3 . Percentage liver
lipid was highest in fish fed the diet with 16.7 kJrg, and the lowest liver lipid was present in fish fed the lowest energy diets. Percentage muscle protein had a narrow
Table 3 Protein and lipid composition of liver and muscle tissues from red drum fed diets containing different energy
levels
a,b b,c
Liver Muscle
Ž . Ž .
Ž . Ž .
Diet designation Protein
Lipid Protein
Lipid
d,f
45 CP: 15.1 kJ 12.3
21.7 20.0
1.8
f
45 CP: 15.9 kJ 12.4
21.4 19.6
1.5
e
45 CP: 16.7 kJ 11.2
30.0 20.4
1.6
f
45 CP: 17.6 kJ 11.6
24.5 20.2
2.4
f
45 CP: 18.4 kJ 10.8
23.3 19.8
1.4 Analysis of variance, P F
0.0565 0.0303
0.8372 0.4608
Pooled standard error 0.38
1.70 0.51
0.32
a
Values represent means of five pooled livers from fish in each of three replicate aquaria.
b
Values are expressed on a fresh-weight basis.
c
Values represent means of individual muscle samples from fish in each of three replicate aquaria.
d
Ž .
Ž .
Values within the same column having different superscripts e,f are significantly different P - 0.05 as determined by Duncan’s multiple-range test.
Ž .
range 19.6 to 20.4 and was not significantly different among fish fed the various diets. Muscle lipid concentration was relatively low for fish fed all diets and was not
significantly different among any groups.
3.1.3. Ammonia production Ammonia production tended to decrease with an increase in dietary energy although
Ž .
only significantly so at 6 h postprandial Table 4 . At almost all time points, the highest dietary energy level resulted in lower ammonia production than the lowest dietary
energy level but this trend was significant only at 6 h.
3.1.4. Plasma glucose and hepatic enzyme actiÕities Plasma glucose levels ranged from 82 to 125 mgrdl and there were no significant
differences attributable to dietary energy density. Activity of GLDH ranged from 23.6 to Ž
. 33.5 molr min mg protein with no significant differences attributable to dietary energy
level. Glutaminase and glutamine synthetase activities also were not significantly Ž
affected by dietary energy, ranging from 4.2 to 8.6 and 2.3 to 4.5 molr min mg .
protein , respectively. 3.2. Effects of nutrient density at different feed rates
3.2.1. Fish growth and body condition indices In the second experiment, there were no differences in survival of red drum based
upon dietary nutrient density and feeding rates with survival ranging from 81 to 94. Increasing nutrient density above that of the 33r13 at 6 resulted in significantly
increased weight gain of red drum although no improvements were made as nutrient Ž
. density increased above that of the 40r15.5 at 5 treatment Table 5 . The 40r15.5 at
satiate treatment resulted in practically identical weight gain as fish fed this diet at a
Table 4 Ammonia produced by red drum fed diets containing various energy levels as measured by aquarium ammonia
Ž Ž
.. levels mgr l kg BW
at 2-h intervals postprandial. Values represent the mean of three replicate aquaria at each time point. Adjustments are made for nitrification occurring and total fish weight in each aquarium for
expression per kg BW Ž .
Hours postprandial h Diet designation
2 4
6 8
10 12
14 16
a,b
45 CP: 15.1 kJ 0.88
1.59 1.98
2.24 1.94
1.36 1.21
1.12
b,c
45 CP: 15.9 kJ 0.75
1.50 1.65
1.94 1.89
1.43 1.33
1.33
b,c
45 CP: 16.7 kJ 0.64
1.40 1.52
1.88 1.78
1.22 1.07
1.07
c
45 CP: 17.6 kJ 0.62
1.27 1.11
1.45 1.75
1.26 1.15
1.21
c
45 CP: 18.4 kJ 0.63
1.21 1.18
1.43 1.68
1.25 1.13
1.23 Analysis of variance, P F
0.1920 0.1813
0.0093 0.1598
0.8423 0.9627
0.9192 0.7836
Pooled standard error 0.18
0.24 0.31
0.45 0.32
0.40 0.35
0.26
a
Ž .
Ž .
Values within the same column having different superscripts b,c are significantly different P - 0.05 as determined by Duncan’s multiple-range test.
B.B. McGoogan,
D.M. Gatlin
III r
Aquaculture
182 2000
271 –
285
279 Table 5
Production characteristics and body condition indices of red drum fed diets containing increasing protein and energy levels at decreasing feed rates
a b
a,c a,d
e,f e,g
e,h
Ž .
Diet regime Weight gain of initial weight
Percent consumption Feed efficiency
Protein efficiency HSI
IPF ratio MR
i,k j
l l
k
33r13 at 6 628
98 0.61
1.60 1.55
0.23 34.7
j k
k k
j,k
40r15.5 at 5 950
92 0.87
1.90 1.72
0.36 36.7
j j
j k
j
50r18 at 4 986
99 1.08
1.91 1.81
0.58 37.2
j k
j j
k
40r15.5 at satiate 951
99 1.12
2.45 1.72
0.32 37.1
Analysis of variance, P F 0.0009
0.0013 0.0001
0.0001 0.7751
0.0349 0.0593
Pooled standard error 41.8
4.65 0.02
0.03 0.31
0.15 1.21
a
Values represent means of three replicate aquaria of fish with average initial weight of approximately 3 grfish and fed for 8 weeks.
b
Values were determined twice weekly on three replicate aquaria and represent the percent of offered feed consumed after 30 min.
c
g gainrg feed fed.
d
g gainrg protein fed.
e
Values represent means of three fish from each of three replicate aquaria.
f
HSI: liver weight=100rfish weight.
g
IPF ratio: intraperitoneal fat weight=100rfish weight.
h
MR: muscle weight=100rfish weight.
i
Ž .
Ž .
Values within the same column with different superscripts j,k,l were determined to be significantly different P - 0.05 by Duncan’s multiple-range test.
Table 6 Ammonia produced by red drum fed diets with increasing protein and energy levels at decreasing feed rates as
Ž Ž
.. measured by aquarium ammonia levels mgr l kg BW
at 2-h intervals postprandial. Values represent means of three replicate aquaria at each time point. Adjustments are made for nitrification occurring and total fish
weight in each aquarium for expression per kg BW Ž .
Hours postprandial h Diet regime
2 4
6 8
10
a,b b
33r13 at 6 3.54
3.64 4.41
4.83 4.68
c b
40r15.5 at 5 2.36
3.18 4.17
4.72 4.78
c b
50r18 at 4 2.58
3.19 4.32
4.80 5.06
c c
40r15.5 at satiate 2.58
3.35 3.51
4.65 4.79
Analysis of variance, P F 0.0066
0.2184 0.0165
0.9825 0.8835
Pooled standard error 0.55
0.38 0.45
0.76 0.76
a
Ž .
Ž .
Values within the same column having different superscripts b,c are significantly different P - 0.05 as determined by Duncan’s multiple-range test.
fixed 5 BWrday. Feed efficiency was significantly greater for fish in the 50r18 at 4 treatment than either the 33r13 at 6 or 40r15.5 at 5 treatments. Utilization of satiation
feeding resulted in significantly better feed efficiency than feeding the same diet at a fixed 5 BWrday. Protein efficiency trends were similar to feed efficiency with values
of fish in the 33r13 at 6 treatment being significantly poorer than those of fish in the 40r15.5 at 5 and 50r18 at 4 treatments. Feeding to apparent satiation again resulted in
significantly better protein efficiency than feeding the same diet at a fixed 5 BWrday. The IPF ratio was affected by dietary and feeding rate manipulations but the treatments
had no effect on MR and HSI. The highest IPF ratio value was exhibited by fish in the 50r18 at 4 treatment although it was not significantly higher than that of fish in the
40r15.5 at 5 treatment. In addition, IPF ratio values were similar when feeding at a fixed rate vs. feeding to apparent satiation. Fish in the 33r13 at 6 treatment had the
lowest MR value although differences among treatments were not quite significant Ž
. P s 0.0593 .
3.2.2. Ammonia production Ammonia production was significantly higher for fish in the 33r13 at 6 treatment
Ž .
compared to all other treatments at 2 h post-feeding Table 6 . However, at most time points, increasing nutrient density in conjunction with decreasing feed rate had no effect
on ammonia production.
4. Discussion
